Photocatalytic hydrogen production from suspension of spinel powders AMn2O4(A=Cu and Zn)

Two narrow band gap-semiconductors AMn2O4 (A=Cu and Zn) with p-type semiconductivity and crystallising in the spinel structure have been studied for photoassisted hydrogen production by visible light in aqueous solution containing sulfide S2− or sulfite SO32. The highest H2 evolution rate, obtained under illumination with platinized Cu-oxide, was found to be 0.26×10−2 ml mg−1 h−1 in a 0.1 M SO32− alkaline solution and does not depend on specific area. H2 evolves over oxide whereas oxidation of S2− and/or SO32− occurs on platinum that behaves as a counter electrode. When sulfide is used as hole scavenger, the hydrogen production decreases over time and reaches a zero value after 3 h because of the formation of coloured polysulfides Sn2−, which acts as an optical filter and compete with water reduction.